<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>变量-布尔类型</title>
</head>
<body>
    
</body>
<script>
var value1 = "123";
var value2 = 0;
var value3 = null;
var value4;
console.log(Boolean(value1)); //true
console.log(Boolean(value2)); //false
console.log(Boolean(value3)); //false
console.log(Boolean(value4)); //false
</script>
</html>